Sulfate Radical Anion Research Articles

Temperature and Ionic Strength Effects on Some Reactions Involving Sulfate Radical [SO4-(aq)

Sulfate radical anion SO4- was generated by 248 nm laser flash photolysis of K2S2O8 solutions and monitored by time-resolved multipass absorbance at 454 nm. The 320−520 nm absorption spectrum of SO4- was unaffected by up to 2 M added HClO4, under the experimental conditions. Three reactions were investigated: (a) SO4- + SO4- → S2O82-, (b) SO4- + H2O → HSO4- + OH, and (c) SO4- + S2O82- → products. Rate constant kc was too slow to be measured, and only an upper limit was determined: kc ≤ 104 M-1 s-1. Arrhenius parameters were determined at low ionic strength over the range 11.8−74.4 °C: 2ka /e = (4.8 ± 2.0) × 105 exp(−1.7 ± 1.1 kJ mol-1/RT) cm s-1 and kb = (4.7 ± 0.1) × 103 exp(−15.5 ± 0.6 kJ mol-1/RT) M-1 s-1, where e is the SO4- absorption coefficient at 454 nm. At 296 K, the values are in good agreement with literature values: 2ka/e = (2.5 ± 0.2) × 105 cm s-1 and kb[H2O] = 440 ± 50 s-1. Rate constants ka and kb were found to increase strongly and nonlinearly with increasing ionic strength (added NaCl...

Spin-trapping studies of the reaction of the sulfate radical anion with N 1-substituted pyrimidine bases. Comparison with continuous-flow electron paramagnetic resonance experiments

Photolysis of K2S2O8-containing solutions of N1-substituted pyrimidines (1-methyluracil, 1-MU; 1, 3-dimethyluracil, l, 3-DMU;1-methylthymine, 1-MT;1, 3-dimethylthymine, 1,3-DMT;1-methylcytosine, 1-MC; 2′-deoxycytosine, dC), together with the spin trap 2-methyl-2-nitrosopropane (MNP) resulted in the EPR spectra of persistent nitroxyl radicals. They were due to spin adducts of 5-hydroxy-5, 6-dihydropyrimidin-6-yl radicals for 1-MU and 1, 3-DMU and to 4-hydroxy-5, 6-dihydropyrimidin-5-yl radicals for 1-MT and 1, 3-DMT. Spectra obtained from 1-MC and dC were tentatively assigned to ring-opened products. Spin-trapped phosphate adduct radicals generated in the presence of HPO42– were characterized by β-nitrogen and β-proton hyperfine splittings and/or by signal intensities. These results are consistent with one-electron oxidation of the substrates by SO4˙– and rapid reaction of the ensuing base radical cations with water or phosphate. Secondary reactions such as oxidation of 5-hydroxy-5, 6-dihydrouracil-6-yl radicals by S2O82– or rearrangement of 5-phosphate-5, 6-dihydrouracil-6-yl radicals complicating the interpretation of previously reported continuous flow EPR spectra (see ref. 22), were not observed in the spin-trapping experiments.

Laboratory studies of atmospheric aqueous-phase free-radical chemistry: kinetic and spectroscopic studies of reactions of NO3 and SO4 ? radicals with aromatic compounds

Recent results from kinetic and spectroscopic laboratory studies of reactions of free radicals such as NO3 and SO4– with aromatic compounds in aqueous solution at T= 298 K are presented. Three different experimental approaches, (i) laser photolysis–visible long-path laser absorption, (ii) laser photolysis–UV long-path laser absorption and (iii) time-resolved broadband diode-array spectroscopy, have been used to investigate the kinetics of reactions of NO3 and SO4– with aromatics, as well as the formation of oxidation intermediates.For the reactions of NO3 with benzene (1), anisole (2), p-xylene (3), p-cresol (4), toluene (5), mesitylene (6) and 1,4-dimethoxybenzene (7), rate coefficients of k1=(4.0 ± 0.6)× 108 l mol–1 s–1, k2=(1.0 ± 0.4)× 109 l mol–1 s–1, k3=(1.6 ± 0.1)× 109 l mol–1 s–1, k4=(8.4 ± 2.3)× 108 l mol–1 s–1, k5=(1.2 ± 0.3)× 109 l mol–1 s–1, k6=(1.3 ± 0.3)× 109 l mol–1 s–1 and k7=(1.0 ± 0.3)× 109 l mol–1 s–1 were obtained. For the corresponding reactions of SO4– with benzene (8), toluene (9), p-xylene (10), p-cresol (11) and mesitylene (12), rate coefficients of k8=(6.4 ± 2.5)× 108 l mol–1 s–1, k9=(1.3 ± 0.6)× 109 l mol–1 s–1, k10=(2.7 ± 0.9)× 109 l mol–1 s–1, k11=(2.8 ± 0.8)× 109 l mol–1 s–1 and k12=(1.3 ± 0.4)× 109 l mol–1 s–1 were determined. Reactivity correlations for both radical species with the aromatic compounds are presented and potential applications of such correlations are discussed. In addition, the effect of ionic strength in the reactions of NO3 with benzene and toluene has been investigated. Transient intermediates have been spectroscopically identified in the reactions of the sulfate radical anion in aerated as well as in oxygen-free solutions. The nature of these intermediates is discussed in view of the existing literature. Finally, possible impacts of free-radical reactions with aromatic compounds on the current understanding of chemical conversion processes within tropospheric multiphase systems are considered.

Electron spin resonance study of the reaction of SO4˙–with azolinones

The reactions of photolytically generated sulfate radical-anion, SO4˙–, with several nitrogen-containing heterocycles of the azolinone type in aqueous solutions were studied by ESR spectroscopy. SO4˙– reacts by formal hydrogen abstraction from an NH group to yield neutral radicals in acidic and neutral solutions and the respective radical-anions at basic pH. The pKa-values of radicals derived from 2,3-dihydroimidazol-2(1H)-one, 2-oxo-2,3-dihydro-1H imidazole-4-carboxylic acid and 2,3-dihydroindazol-3(1H)-one were determined to be in the range 8.5–10.4. In the cases of 2,3-dihydroimidazol-2(1H)-one and 2,3-dihydropyrazol-3(1H)-one secondary radicals were detected at basic pH. These radicals resulted from the disproportionation of the primary radicals followed by addition of OH– and oxidation of the OH-adduct.

Free-radical aqueous slurry polymerizations of acrylonitrile: 2. End-groups and other minor structures in polyacrylonitriles initiated by potassium persulfate/sodium bisulfite

Polyacrylonitriles prepared by aqueous free-radical slurry polymerization using the potassium persulfate/sodium bisulfite redox initiation system have been examined by FT i.r. and high-field 13C and 1H n.m.r. spectroscopy. They have been shown to contain predominantly sulfonate and non-sulfur containing end-groups derived principally from initiation by bisulfite radicals and transfer to the bisulfite ion. Some sulfate end-groups are present also, although in much smaller amounts than the sulfonate end-groups, and are believed to arise from initiation by sulfate radical anions. In these respects, the polymers resemble closely those made by using ammonium persulfate/sodium metabisulfite as the initiator system.

Free-radical aqueous slurry polymerizations of acrylonitrile: 1. End-groups and other minor structures in polyacrylonitriles initiated by ammonium persulfate/sodium metabisulfite

Polyacrylonitriles prepared by aqueous free-radical slurry polymerization at 40°C using ammonium persulfate and sodium metabisulfite as redox initiator have been examined by FTi.r. and by high-field 13C and 1H n.m.r. They have been shown to contain small quantities of acrylamide and acrylic acid units and to possess predominantly sulfonate and non-sulfur containing end-groups derived principally from transfer to bisulfite ion during the polymerization. Other end-groups present in low concentration are sulfate and hydroxyl; the former probably arises from initiation by sulfate radical anions and the latter either from transfer to water or by adventitious hydrolysis of some of the sulfate end-groups. Because they contain few groups capable of initiating intramolecular cyclization, the polyacrylonitriles are white with no sign of discoloration.

Induction of strand breaks in polyribonucleotides and DNA by the sulphate radical anion: role of electron loss centres as precursors of strand breakage.

The interaction of the sulphate radical anion, SO4.-, with the polyribonucleotides, poly U and poly C, in deaerated, aqueous solutions at pH 7.5 results in strand breakage (sb) with efficiencies of 57 and 23%, respectively, determined by time resolved laser light scattering (TRLS). Most sb are produced within 70 microseconds, the risetime of the detection system. Oxygen inhibits the induction of sb in poly U and poly C by SO4.- through its interaction with a radical precursor to sb. In contrast, the interaction of SO4.- with poly A and single stranded DNA does not lead to significant strand breakage (< or = 5% efficiency). From optical studies, the interaction of poly A and poly G with SO4.- radicals yields predominantly the corresponding one electron oxidized base radicals. With poly C and poly U, it is proposed that the SO4.- radical interacts predominantly by addition to the base moiety to produce the C(5)-yl and C(6)-yl sulphate radical adducts which react with oxygen. These base adducts subsequently interact with the sugar-phosphate moiety by H-atom abstraction to yield C(2)' sugar radicals with rate constants in the range 1.3-1.7 x 10(5) s-1. It is proposed that the C(2)' sugar radical leads to strand breakage within 70 microseconds, in competition with its transformation into the C(1)'-sugar radical involving base release. From optical studies on the interaction of SO4.- with double stranded DNA, it is suggested that the predominant radical species produced in DNA is the one-electron oxidized radical of guanine, consistent with positive charge migration in DNA. Since the efficiency of SO4.- to induce sb in single stranded DNA is low, it is concluded that the one-electron oxidized guanine radical does not effectively induce strand breakage in DNA.

Electron transfer reaction rates and equilibria of the carbonate and sulfate radical anions

Electron transfer reactions of the carbonate radical anion with azide, bromide, and hypochlorite ions have been studied by pulse radiolysis. From the equilibrium Br .- 2 + CO 2- 3 ⇆ 2Br - + CO .- 3 and the known redox potential for Br .- 2/2Br - = 1.62V vs NHE we derive E = 1.59V for CO .- 3/CO 2- 3. From this value and the equilibrium CO .- 3 + ClO - ⇆ CO 2- 3 + ClO . we derive E = 1.41V for ClO ./ClO -. The equilibrium reaction SO .- 4 + Cl - ⇆ SO 2- 4 + Cl . was studied by laser photolysis, by using 248 nm excitation of S 2O 2- 8 to produce SO .- 4 and examining the rate of reaction of this radical with Cl - in the presence of varying concentrations of SO 2- 4. By modeling the reactions taking place in this system, we derive the rate constant for the reaction of Cl . with SO 2- 4 (2.5 × 10 8dm 3mol -1s -1 at 0.1 mol dm -3 ionic strength), and from the known rate constant for reaction of SO .- 4 with Cl - (4.7 × 10 8dm 3mol -1s -1 at the same ionic strength) we derive the equilibrium constant. From the known redox potential for Clf .- 2/Cl - = 2.41V we derive E = 2.43V for SO .- 4/SO 2- 4.

ChemInform Abstract: Kinetics of the Reactions of the SO‐ 4 Radical with SO‐ 4, S2O2‐ 8, H2O and Fe2+.

AbstractThe optical absorption spectrum (270‐500 nm) of the sulfate radical anion, SO4‐, is obtained following laser photolysis of K2S2O8 solutions at 248 nm and its decay in the presence of S2O82‐ and Fe(II) is investigated using kinetic spectrophotometric techniques.

ChemInform Abstract: Kinetics and Mechanism of the Reduction of Hydroxylamine‐O‐sulfonic Acid by the Hexaaquochromium(II) Ion.

The title reaction takes place with a 2:1 (Cr{sup 2+}):(HSA) stoichiometry (HSA = hydroxylamine-O-sulfonic acid) and yields CrNH{sub 3}{sup 3+}, Cr{sup 3+}, and CrSO{sub 4}{sup +} as the main products. The kinetics conform to the rate law {minus}d(HSA)/dt = {minus}d(Cr{sup 2+})/2(dt) = k{sub obs}(Cr{sup 2+})(HSA), where k{sub obs} = kK{sub a}/(K{sub a} + (H{sup +)}). At 25{degree}C and 1.0 M ionic strength (CHlO{sub 4} + LiClO{sub 4}) the parameter k has the value of 20.5 {plus minus} 0.3 M{sup {minus}1} s{sup {minus}1} when K{sub a} is set at the value (6.8 {plus minus} 0.8) {times} 10{sup {minus}2} M, as determined by pH titration. In the proposed mechanism, Cr{sup 2+} attacks at the nitrogen end of the anion, NH{sub 2}OSO{sub 3}{sup {minus}}, to form CrNH{sub 3}{sup 3+} and SO{sub 4}{sup {center dot}{minus}}. The sulfate radical anion then oxidizes rapidly the second mole of Cr{sup 2+} to yield Cr{sup 3+} and some CrSO{sub 4}{sup +}. In solutions containing Br{sup {minus}}, SO{sub 4}{sup {center dot}{minus}} oxidizes it to Br{sub 2}{sup {center dot}{minus}}. The latter reacts with Cr{sup 2+} to yield CrBr{sup 2+}. 19 refs., 2 figs.

Kinetics and mechanism of the reduction of hydroxylamine-O-sulfonic acid by the hexaaquochromium(II) ion

The title reaction takes place with a 2:1 (Cr{sup 2+}):(HSA) stoichiometry (HSA = hydroxylamine-O-sulfonic acid) and yields CrNH{sub 3}{sup 3+}, Cr{sup 3+}, and CrSO{sub 4}{sup +} as the main products. The kinetics conform to the rate law {minus}d(HSA)/dt = {minus}d(Cr{sup 2+})/2(dt) = k{sub obs}(Cr{sup 2+})(HSA), where k{sub obs} = kK{sub a}/(K{sub a} + (H{sup +)}). At 25{degree}C and 1.0 M ionic strength (CHlO{sub 4} + LiClO{sub 4}) the parameter k has the value of 20.5 {plus minus} 0.3 M{sup {minus}1} s{sup {minus}1} when K{sub a} is set at the value (6.8 {plus minus} 0.8) {times} 10{sup {minus}2} M, as determined by pH titration. In the proposed mechanism, Cr{sup 2+} attacks at the nitrogen end of the anion, NH{sub 2}OSO{sub 3}{sup {minus}}, to form CrNH{sub 3}{sup 3+} and SO{sub 4}{sup {center dot}{minus}}. The sulfate radical anion then oxidizes rapidly the second mole of Cr{sup 2+} to yield Cr{sup 3+} and some CrSO{sub 4}{sup +}. In solutions containing Br{sup {minus}}, SO{sub 4}{sup {center dot}{minus}} oxidizes it to Br{sub 2}{sup {center dot}{minus}}. The latter reacts with Cr{sup 2+} to yield CrBr{sup 2+}. 19 refs., 2 figs.

Mechanisms of peroxide decomposition: an electron paramagnetic resonance study of the reaction of the peroxomonosulphate anion (HOOSO ? 3 ) with CuI. A marked contrast in behaviour with that of TiIII and FeII

EPR spectroscopy has been employed in conjunction with a continuous-flow system to show that CuI(produced from the rapid reaction of CuII with TiIII) reacts rapidly with the peroxomonosulphate anion (k≈ 2 × 104 dm3 mol–1 s–1 at pH 2 and 20 °C) to give the hydroxyl radical (HO˙) which is trapped via its addition to alkenes. In contrast, FeII and TiIII react with HOOSO–3 predominantly to give the sulphate radical-anion (SO˙–4). It is argued that with CuI the reaction shows characteristics of an outer-sphere electron-transfer process, whereas in the inner-sphere reaction of FeII and TiIII the reaction is facilitated by attack of the hydroxyl oxygen atom on the smaller, more highly charged metal ions.

Sulfate anion free radical formation by the peroxidation of (Bi) sulfite and its reaction with hydroxyl radical scavengers

The one-electron oxidation of (bi) sulfite is catalyzed by peroxidases to yield the sulfur trioxide radical anion (SO − 3), a predominantly sulfur-centered radical as shown by studies with 33S-labeled (bi)sulfite. This radical reacts with molecular oxygen to form a peroxyl radical. The subsequent reaction of this peroxyl radical with (bi)sulfite has been proposed to form the sulfate anion radical, which is nearly as strong an oxidant as the hydroxyl radical. We used the spin trapping electron spin resonance technique to provide for the first time direct evidence for sulfate anion radical formation during (bi)sulfite peroxidation. The sulfate anion radical is known to react with many compounds more commonly thought of as hydroxyl radical scavengers such as formate and ethanol. Free radicals derived from these scavengers are trapped in systems where (bi)sulfite peroxidation has been inhibited by these scavengers.

Electron spin resonance studies. Part 69. Oxidation of some aliphatic carboxylic acids, carboxylate anions, and related compounds by the sulphate radical anion (SO4–˙)

The results of e.s.r experiments involving in situ photochemical generation of the sulphate radical anion in the presence of some aliphatic carboxylic acids and their anions are interpreted in terms of attack at the carboxy group (to give alkyl radicals via decarboxylation) and hydrogen-atom abstraction from carbon atoms in the chain. The general order of reactivity of different sites is CO2– > β-H, γ-H, etc. > CO2H > α-H. For example, reaction with EtCO2H gives ˙CH2CH2CO2H (k 2 × 105 dm3 mol–1 s–1) and Et˙(k 7 × 104 dm3 mol–1 s–1). Radicals formed by abstraction of α-H (e.g.˙CH2CO2H from ethanoic acid) are shown to result usually from further reactions of first-formed alkyl radicals. The reactions of SO4–˙ with some amides, nitriles, and esters have also been investigated.

Alkene oxidatioh by an iron(II)/persulfate/acetic acid system

Mono- and disubstituted alkenes were converted to trans-vicinal diacetates by heating with an iron(II)/persulfate/acetic acid system. The synthetic utility and limitations were identified. A mechanism for the transformation is proposed which involves an initial addition of sulfate radical anion to the alkena followed by solvolysis, addition, hydrolysis, and aoetylation.

Electron-transfer processes: oxidation of α- and β-alkenylbenzenes by peroxydisulphate in acetic acid

Oxidation of α- and β-unsaturated alkylbenzenes by peroxydisulphate in acetic acid gives side-chain acetoxylation with formation of the corresponding glycol diacetates and compounds (10), respectively. The reaction is catalysed by transition-metal salts, among which cupric acetate gives the best results. Generally, electron-releasing substituents on the benzene ring increase the yield and improve the selectivity. The same substrates are oxidized in water under Ag+ catalysis to the corresponding aldehydes. The different behaviour in the two solvents is ascribed to the difference in reactivity between the primary oxidation products and the starting olefin, whereas the initial oxidation step is suggested to occur in both cases via an electron-transfer process from the olefin to the sulphate radical anion.

Evidence that N-acetoxy-N-acetyl-2-aminofluorene crosslinks DNA to protein by a free radical mechanism.

A method was devised to quantitate N-acetoxy-N-acetyl-2-aminofluorene (N-AcO-AAF) induced crosslinking of the ionic complex between [methyl-3H]thymidine labeled pBR322 DNA and lysozyme. This involved chromatography of the modified complex on Sephadex CM 25 with a high salt buffer that dissociated the non-covalently bound complex and permitted early elution of unbound [3H]DNA. The crosslinked complex was then eluted with buffer at pH 10.5. The amount of crosslinking was a function of the carcinogen concentration in the reaction mixture containing the complex. Addition of the spin trap nitrosobenzene or the radical trap 2,2-diphenyl-1-picrylhydrazyl to the complex prior to the addition of N-AcO-AAF decreased crosslinking. Reaction of the carcinogen with a solution of [methyl-3H]thymidine labeled Escherichia coli DNA led to the formation of tritiated water that was azeotropically distilled from the mixture. If nitrosobenzene was added prior to the carcinogen, the amount of tritium water released was depressed. Addition of N-AcO-AAF to a mixture of acrylamide and bisacrylamide increased its relative viscosity. Far u.v. irradiation of the complex or reacting it with ammonium persulfate that dissociates to the sulfate anion radical, SO(4), induced crosslinking. While these observations support a free radical mechanism for crosslinking, whether the free radicals arise from heterolytic or homolytic cleavage of N-AcO-AAF remains undetermined.

Reduction of peroxomonosulfate by oxovanadium(IV) in acidic solution. Role of the sulfate radical anion

Reduction of peroxomonosulfate by oxovanadium(IV) in acidic solution. Role of the sulfate radical anion

The mechanism of reaction of sulfate radical anion with some derivatives of benzoic acid

The products of the reactions of SO/sub 4//sup -/ with some benzoic acid derivatives have been examined by ESR using steady-state radiolysis and photolysis to produce SO/sub 4//sup -/ and by optical absorption spectrophotometry in pulse radiolysis experiments. The optical absorption spectrum of the hydroxycyclohexadienyl radical following reaction of benzene with SO/sub 4//sup -/ is shown to be formed with <0.1 ..mu..s delay. Thus it appears that a cation is formed which reacts very rapidly with water. Similarly, pulse ESR methods have been used to show that the p-carboxyphenyl radical is formed within <1 ..mu..s of the reaction of SO/sub 4//sup -/ with terephthalate. With benzoate, most of the reaction leads to the phenyl radical but about 30% gives hydroxycyclohexadienyl radicals. The three isomeric toluates give different products. The ortho isomer gives mainly the o-carboxybenzyl radical while the para isomer gives approximately equal amounts of p-carboxybenzyl, p-methylphenyl, and a mixture of hydroxycyclohexadienyl radicals. The meta isomer gives mainly a mixture of hydroxycyclohexadienyl radical isomers. Several carboxyphenols were studied by ESR and all gave phenoxyl radicals. All reactions observed are consistent with the oxidation of the benzene ring to a cationic species which then reacts in parallel reactions by either hydroxylation,more » loss of a proton (from OH or CH/sub 3/ groups), or loss of CO/sub 2/.« less

Rate constants and mechanism of reaction of sulfate radical anion with aromatic compounds

Absolute rate constants for reaction of .SO/sub 4//sup -/ with substituted benzenes and benzoates have been determined by pulse radiolysis. The values are found to range from about 5 x 10/sup 9/ M/sup -1/ s/sup -1/ for anisole to less than 10/sup 6/ M/sup -1/ s/sup -1/ for nitrobenzene. A correlation of the rate constants with the Hammett substituent constant sigma gave rho = -2.4 for both series of compounds. It is concluded that the reaction takes place by an electron transfer from the ring to .SO/sub 4//sup -/.